Prevention and control measures of chicken typhoid

Chicken typhoid is a septic infectious disease of poultry caused by salmonella, which mainly occurs in chickens and turkeys. The course of disease is acute or chronic. The mortality rate is related to the virulence of the pathogen.

Chicken typhoid is distributed worldwide, and the damage caused by the disease is very serious, with a mortality rate of 10% 50% or more. Salmonella can infect chickens of any age. According to Hall and others, the 1-6-month-old mortality rates of chicken farms with chicken typhoid fever were 25.6% 13, 5% 24.9%, 19.2%, 13.8% and 2.7%, respectively. The eggs of breeder chickens infected with salmonella can be transmitted vertically. After culturing 1000 eggs laid by natural and artificially infected chickens, Hall and others found that 50% of the eggs laid by typhoid positive chickens were contaminated. Of the 906 chicks hatched with these positive eggs, 296 (32.6%) died of the disease in the first 6 months, with the most serious death in the first month.

Disease pathogen

The pathogen of chicken typhoid is Salmonella gallinarum, which is short, thick and rod-shaped, with a size of 1.0-2.0 × 1.5 μ m, often scattered alone and occasionally in pairs. Gram staining is negative, no spores, no capsule, no flagellum.

Salmonella chicken is easy to grow on pH7.2 beef extract Agar, beef extract Agar and other nutrient media, aerobic and facultative anaerobic, and grows best under the condition of 37 ℃. The strain could grow on selenate and tetrasulfonic acid broth, and could grow on McConkey, bismuth sulfite, SS, deoxycholate, deoxycholate, lactose citrate sucrose and bright green Agar.

The bacteria formed small, moist, round blue-gray colonies on nutrient Agar with neat edges. Grow in broth to form flocculent deposits.

For the biochemical characteristics of chicken salmonella, see "Chicken White dysentery".

The pathogen was killed in 60 ℃ for 10 minutes and in direct sunlight for a few minutes; 0.1% carbolic acid and 1% potassium permanganate could kill it in 3 minutes; and 2% formaldehyde solution could kill it in 1 minute. The bacteria can survive for a long time under some conditions, such as 20 days in dark water, and the highly virulent salmonella can be isolated from the bone marrow of chickens who died of chicken typhoid fever 3 months later.

The O antigen of Salmonella gallinarum is 1mem9 and 12, and the antigenicity of O12 has no variation, which is different from Salmonella pullorum.

Epidemiology

Chicken cold occurs not only in chickens and turkeys, but also in ducks, guinea fowls, peacocks, quails, grouse, pheasants and so on. Chickens of all ages can be infected.

Diseased chickens and infected chickens are the main sources of infection. There are many ways of transmission. The keeper's clothes, shoes and hats, transport vehicles, appliances, wild birds, flies and so on can mechanically transmit pathogens. Digestive tract is the main route of infection.

The disease can also be transmitted vertically. For example, Rao and others isolated and cultured 36 eggs laid by positive chickens, of which 13 (36%) were isolated from chicken salmonella. Hall et al hatched with eggs laid by positive chickens, and 296 (32.6%) of the 906 chicks hatched died of typhoid fever in the first six months.

Clinical symptoms

The symptoms of chicks and turkeys are similar to those of chicken pullorum. Contaminated breeding eggs can hatch weak chicks and dead chicks. Infection after hatching, the incubation period is 4-5 days, and the performance after onset is the same as that of pullorum.

After the onset of the disease, young or adult chickens initially showed mental distress, loose feathers, pale head, shrunken chicken crown and a sharp decrease in feed consumption. Within 2-3 days after infection, the body temperature increased by 1-3 ℃ and lasted until a few hours before death.

When turkeys have an outbreak of typhoid fever, they are characterized by increased thirst, loss of appetite, mental malaise, isolation, and excretion of green or yellow dung. The body temperature increased to 44-45 ℃.

Mechanism pathology

In acute chicken typhoid, there is severe hemolytic anemia. This is due to changes in red blood cells affected by endotoxin and eliminated by the reticuloendothelial system.

The tissue pathological changes of the most acute cases were not obvious, and the longer course of the disease showed redness and swelling of liver, spleen and kidney. these lesions were common in young chickens. In subacute and chronic cases, the liver is often enlarged, greenish brown or bronze. In addition, there are miliary gray-white lesions in the liver and myocardium, pericarditis, peritonitis caused by egg rupture, egg bleeding, deformation and color change, catarrhal enteritis. After infection, grayish-white necrotic foci can be seen in the lungs, heart and myogastric muscles. The pathological changes of turkeys are similar to those of chickens.

Prevention and cure measures

When the occurrence of chicken typhoid fever, timely isolation of diseased chickens, dying chickens and chicken droppings for deep burial or burning treatment, diseased chickens and large flocks of chickens for drug treatment. Sulfonamides are selected for treatment, in addition, the sanitary disinfection of eggs, hatching and brooding should be strengthened, and the feeding management and cleaning and disinfection of utensils should be strengthened at ordinary times.